The present invention relates generally to aircraft ventilation mechanisms and more particularly to an aircraft ventilation mechanism having a door that may be positioned in a flush open position.
In the design of auxiliary air inlet doors, several design goals must be considered. One such goal relates to the pressure drop that results from the (partial) blockage of the duct when the door is fully opened. When the aircraft is on the ground, it is frequently desirable to open the door as far as possible so as not to induce a pressure drop. This is particularly important, for example, when the air inlet door is used to selectively control the flow of air to a conventional auxiliary power unit (xe2x80x9cAPUxe2x80x9d) having a gas turbine engine. This is because the gas turbine engine of the APU will not operate properly if the pressure drop that results from the blockage of the duct sufficiently limits the amount of air that may be drawn into the engine. In extreme cases, the pressure drop may cause an insufficient amount of air to be drawn into the gas turbine engine and prevent the auxiliary power unit from operating.
Another goal relates to the amount by which the door extends into the free stream airflow. Minimizing the extent to which the door projects into the free stream airflow improves the aerodynamics of the aircraft, reduces the amount of noise that is transmitted to the cabin of the aircraft, and reduces concerns associated with the formation of ice on the door. Due to the conflicting nature of these goals, the design of auxiliary inlet doors is usually a compromise of various factors with the designer trading one performance aspect for another until the total result satisfies all of the design criteria to the extent possible.
One suggested solution is a xe2x80x98bicycle seatxe2x80x99 vane which is mounted externally on the auxiliary door. The xe2x80x98bicycle seatxe2x80x99 vane acts as a vortex generator to enhance ram recovery without requiring a wide opening scoop-shaped door. However, the vane is quite prominent and generates some aerodynamic drag even when the door is closed.
Another suggested solution is a long NACA flush scoop with a moving ramp to close the inlet opening. While this arrangement minimizes drag, the ram recovery is negatively affected because the inlet is immersed in the thick airstream boundary layer at the aft end of the fuselage. Some of these arrangements have problems with fluids that may leak from the airplane, as these fluids tend to migrate along the fuselage belly where they are ingested by the scoop. Generally, these scoops are also less compact and heavier than conventional auxiliary doors.
It is one object of the present invention to provide an air inlet mechanism having high ram recovery.
It is a further object of the present invention to provide an air inlet mechanism having relatively little aerodynamic drag when an inlet door is placed in a fully opened position.
It is yet another object of the present invention to provide an air inlet mechanism which produces a relatively small pressure drop in an duct connected to the air inlet mechanism when a door structure is placed in a fully opened position.
In one preferred form, the present invention provides an air inlet mechanism having a housing and a door structure. The housing includes a body portion with a fluid conduit formed therethrough. The body portion also includes a wall member that defines an end wall with at least a portion of the endwall being concave in shape such that a recessed cavity is formed in the fluid conduit. The door structure is pivotably coupled to the housing and movable between a closed position substantially closing the fluid conduit and an open position wherein the door structure is disposed within the fluid conduit. The recessed cavity receives at least a portion of the door structure when the door structure is moved between the closed position and the open position. Construction in this manner provides an air inlet mechanism having relatively high ram recovery when the door structure is placed in a ram position, relatively little aerodynamic drag when the door structure is placed in a closed position, and relatively little back pressure (i.e., blockage) of a duct structure when the door structure is placed in the open position.